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B. trachona is a crustose lichen of shady, siliceous rock habitats such as overhung, lough shore and tarn-edge margins. It is here that it often grows with B. carneoglauca in tiny rock caves where it can spread to tree roots. Commonly, B. trachona is found without discs. The thin, grey-green (Pd+ red) thallus is minutely granular and peppered with conspicuous black pycnidia. Discs, when present, are flat, black with a K+ purple, dark red-brown hypothecium. In Ireland the species is known from Counties Kerry, Donegal and Antrim.